1. Field of the Invention
The present invention relates to a wet processing apparatus used in the manufacture of semiconductor devices.
2. Description of the Related Art
In the manufacture of semiconductor devices, wet processing steps are so essential that the manufacturing yield of semiconductor devices is dependent thereupon. For example, one wet processing step cleans surfaces of wafers to remove contamination therefrom. Other wet processing steps remove photoresist in a photolithography step, etch a semiconductor region in a semiconductor region forming step, etch an insulating layer in an insulating layer forming step, and etch a metal layer in a metal layer forming step. These wet processing steps use a large amount of chemicals such as organic solvent, strong acid and strong alkali.
The wet processing steps are mainly divided into three steps: a cleaning step, an etching step and a rinsing step. For example, in a cleaning and rinsing step, contamination, organic or inorganic particles, residual resist and ionic residue are removed from a surface of a wafer without affecting the wafer. In this case, chemicals using a mixture of 27 percent NH.sub.4 OH, 30 percent H.sub.2 O.sub.2 and water having a ratio of 1:1:6 are used. Also, in an etching step, the wafer is etched, or a natural oxide layer or an organic layer on the wafer is etched.
In the above-mentioned wet processing steps, large amounts of discarded chemicals are to be processed, and therefore, large scale equipment and running costs are required. That is, used pure water is reactivated by a closed system to recover pure water. Used chemicals are also reactivated until they are used up, and they are finally decomposed and neutralized, and then discarded.
In view of the foregoing, in order to drastically reduce the amount of chemicals used, a wet processing apparatus has been proposed by Japanese Patent Application No. HEI5-105991 filed on Apr. 9, 1993. This wet processing apparatus includes an electrolytic cell for generating anode active water and cathode active water, a first processing cell for processing a target with the anode active water, a second processing cell for processing a target with the cathode active water, and a used water cell for storing the used water of the first and second processing cells. Also, a reactivating feedback path formed by a water treatment unit and an ion exchange unit is provided between the used water cell and the electrolytic cell, so that the used water is reactivated and fed back to the electrolytic cell. This will be explained later in detail.
In the above-described proposed wet processing apparatus, however, since the used anode water and the used cathode water are merged in the used water cell, H.sup.+ ions of the anode water and OH- ions of the cathode water are neutralized, so that more supporting electrolyte or the like has to be added to the merged water before the electrolytic cell. This is disadvantageous in that it prevents a reduction of chemicals.
Also, in the above-described proposed wet processing apparatus, since the electrolytic water of the electrolytic cell is directly supplied to the processing cells, the electrolytic cell has to be enlarged. Also, the electrolyte is easily deteriorated.
Further, in the above-described proposed wet processing apparatus, the deterioration of electrolyte cannot be completely monitored.